Glucose-6-phosphate transporter and receptor functions of the glucose 6-phosphatase system analyzed from a consensus defined by multiple alignments

The cDNA encoding the protein (P46) that is mutated in glycogen storage dis ease type-1b (GSD-1b) has been previously cloned by homology with bacterial sequences of the uhp (upper hexose phosphate) system. Hydropathic profiles , transmembrane-prediction analysis, and a multiple alignment of 14 sequenc es related to P46 (with percentage of identity around 30%) allowed to ident ify two large domains in the proteins linked by a large variable loop. High ly conserved transmembrane (TM) segments, TM1 and TM4 in the first domain a nd TM5 in the second one, were identified almost in all the integral protei ns related to P46. The multiple alignment allowed definition of a consensus involving the 14 sequences related to P46. The detailed comparison of the consensus with the UhpT (the bacterial G6P transporter) and with UhpC (the bacterial G6P receptor) sequences reveals that the P46 protein could carry both G6P receptor and transporter functions. Proteins 2000;41:164-172, (C) 2000 Wiley-Liss, Inc.